It has become increasingly prevalent to package food and other products in non-metallic containers, such as containers and pouches made from thermoplastic material. One problem which arises with the usage of these materials is that many non-metallic materials, such as paper or thin films of polymeric materials, including polyethylene, are sufficiently permeable or porous to allow diffusion of atmospheric oxygen from the exterior of the container or package into the interior of the container.
In the packaging of many food products and other commercial products which are sensitive to or reactive with oxygen, it would be desirable to provide an inexpensive structural material which would effectively decrease the penetration of oxygen through the container wall. The contamination of food products as well as other commercial products with oxygen after packaging has many undesirable effects, including discoloration, deterioration, and spoilage of the product, resulting in significant loss in acceptable commercial shelf storage life.
It is well known in the plastics art and the commercial process of packaging products to incorporate minor concentrations of certain antioxidants into the polymer before polymerization, extrusion or other formation thereof, as well as to coat plastic and paper films with subsequent film layers which contain antioxidants. Such antioxidants tend to prevent oxidation of, and change of properties in, the polymer itself but do not actively react with oxygen.
C. W. Desaulniers, in U.S. Pat. No. 3,499,820, issued Mar. 10, 1970, discloses a self-supporting laminate of polymeric films, including a first film of polymer, and a second film bonded to the first film and containing a filler of clay-like mineral having plate-like shapes. A third film of polymer is disposed adjacent to the second filler film. The self supporting laminate provides low permeability to gases, specifically oxygen, by mechanically interposing a plate-like mineral barrier film.
C. C. Kirk, T. E. Ferington, and R. S. Gregorian, In U.S. Pat. No. 3,539,437, issued Nov. 10, 1970, disclose a self-supporting laminate film having a first sheet of flexible thermoplastic film, a second sheet of mineral filler selected from minerals consisting of vermiculite, mica, talc, and clay bonded to the first film. At least one additional film of a polymer is disposed on the second film. The bonded multiple ply laminate provides a mechanically impermeable mineral barrier plate-like structure reducing the permeability of gases through the laminate structure.
Schindler, in Austrian Pat. No. 212,209 issued Dec. 12, 1960, discloses a multiple ply laminate having a hydrophilic carrier layer, a layer adjacent to the hydrophilic carrier layer, which is impermeable to water vapor, to fatty substances, and to light and consists of a thermoplastic coating containing pigments of powdered metal and titanium dioxide. A third layer consisting of chlorinated rubber and a synthetic resin is bonded to the second layer, and a fourth layer of synthetic thermoplastic material provides a hardness greater than any of the other layers.
A Russian Pat. No. 238,774, issued July 15, 1969, discloses an inert powder between a pair of parent materials, followed by a thermal welding step. The powders are silicon dioxide, metal oxides and the like.
The Cook U.S. Pat. No. 3,429,717 discloses a multiple-ply film structure containing an organic antioxidant and solvent between two adjacent plies. The types of antioxidants disclosed, such as propyl gallate, however, do not react directly with oxygen and would not serve to chemically react with oxygen being transmitted between the plies.
The Parlour U.S. Pat. No. 2,979,410 and Canadian Pat. No. 569,215 disclose the concept of providing an edible antioxidant coating on the surface of the film that is wrapped over the food product, whereby the surface of the food becomes coated with the antioxidant to prevent deterioration. Certain oxygen reactive and edible compounds, however, such as ascorbic acid, tend to discolor upon being oxidized, thereby imparting ab undesirable color to the packaging or the food.
In accordance with the Supplee U.S. Pat. No. 1,584,903, an oxygen reactive agent such as ferrous sulphate or stannous chloride is provided on an isolated interior wall of a container so as to absorb free oxygen present in the container.